There is a class of medical emergencies for which little, if anything, can be done for the patient. A patient's heart ceases to beat and heroic efforts are undertaken by medical professionals to revive the patient. Very little time elapses before irreparable damage is done to vital organs. These situations occur in operating rooms, in intensive care facilities, and in emergency rooms.
In the operating room, a heart-lung machine may be used to perform heart functions while heart operations are conducted. But such machines cause damage to the blood and can be used only for relatively short periods of time.
Artificial hearts are well known also. But such hearts are only for experimental purposes for implantation, when a human heart no longer performs its critical function of pumping blood to vital organs and has to be replaced or the patient dies. Artificial hearts are designed for internal use and are expensive. Moreover they cause blood clots and infection problems which are as yet unresolved. If no biological heart is available, there is no long term support for the patient except such implantable devices. Available short term pumping devices are approved for use for up to 6 hours and are not designed to be replacement devices for intermediate use for providing the pumping function equal to that of the natural heart. Such short term devices provide only minor support for the heart and do not respond to needs for perfusion nor for meeting human physiological needs.
A variety of heart assist devices is also available. But these devices also have problems. They cause damage to the blood, require the heart to work harder, and also, in some instances, cause clots.
U.S. Pat. No. 4,547,911 issued Oct. 22, 1985 to W. E. Strimling discloses an implantable heart pump which needs no external vent. Because most infections in such devices originate from such a vent, a prime source of infection is eliminated. U.S. Pat. No. 4,468,177 issued Aug. 28, 1984 and U.S. Pat. No. 4,512,726 issued Apr. 23, 1985 disclose implantable heart pumps where the blood chambers are designed to eliminate crevices which produce clotting and the pump motors are driven in a manner to reduce damage to the blood.
In the pump disclosed in the above-mentioned patents and, as is the case in all implantable hearts and heart assist devices, a blood chamber in the device is equiped with inlet and outlet ports operative to admit blood into the chamber when the volume of the chamber is increased and to vacate the chamber when the volume of the chamber is reduced. In the above mentioned patents, the volume of the blood chamber is changed by a motor-driven pusher plate which moves up and down against the bottom of the chamber. A left ventrical assist device would be operative in this manner.
The patents also describe placing the motor and drive mechanism in a chamber located between two blood chambers. Such a device includes two pusher plates operative out of phase with one another. Thus, the volume of one blood chamber decreases while the volume of the other increases. Such an arrangement is useful as a heart replacement.